Our Year Ahead series examines the most important trends, people and companies that will impact science and technology in 2024.
Biologist Andrew Derocher has an unusual nickname for polar bears.
“I call them fat vacuums.”
The nickname stems from their particular way of surviving in one of the most inhospitable environments on Earth. “They go around, kill seals, and suck the fat off and just stick it into their own cells,” said the University of Alberta ecologist. “It’s an incredible process, and they don’t have to kill many seals because they’re just so energy-rich.”
Polar bears’ exceptional capacity to transform seal fat into insulation and energy has allowed these massive creatures to thrive in the Arctic for millennia. But that capacity rests on a crucial — and increasingly imperiled — resource: sea ice. Frozen area is already down by 40% since 1979, and melting is likely speeding up — last summer was the warmest on record in the Arctic. Scientists suspect that the first ice-free Arctic summer could come as soon as the 2030s.
Without sea ice, polar bears can’t reach the seals on which they depend. As climate change transforms the Arctic faster than most other places on Earth, this vital resource is melting from underneath polar bears’ feet. Some regions support only half the polar bears they used to, and all are facing an uncertain future. Perhaps more than any other species, polar bears symbolize climate change’s existential threat to biodiversity, raising questions about the long-term prospects of this icon of winter in a warmer world.
“Overall, it’s a pretty simple story,” said Derocher. As the globe heats up, sea ice will melt, and polar bears will starve. But that simple story also belies complexities, he explains.
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For now, there are about 26,000 polar bears, substantial numbers compared with some other endangered species. While some populations are declining, others are stable, or even growing, as warming opens up areas once too cold for the bears.
If we don’t rein in emissions, polar bears could be nothing more than a distant memory for future generations of humans. But that outcome isn’t set in stone.
“Our best analyses indicate that we will still have polar bears at the end of this century,” said Derocher. “But it’s quite likely that their overall range will be quite reduced, and many populations will disappear.”
THERE ARE 19 different polar bear populations across the Arctic regions of the U.S., Canada, Greenland, Norway and Russia. All are tied, in some form, to the seasonal rhythms of sea ice advance and retreat.
As temperatures drop, sea ice forms and thickens, providing the ground on which bears can venture out onto the sea and hunt in the spring. During this time, they eat as many seals as they can, packing on the fat they’ll need to sustain themselves as the ice recedes and they’re forced back onto land, where they largely fast until they can feed again.
The duration of this period largely determines bear survival from year to year, Derocher explained. “Once you go beyond about 180 days, the bears start to have serious issues,” he said. Younger cubs and older bears are most susceptible to starvation during extended fasting, but all bears have their limit.
“The problem is that as that ice-free period gets longer, more bears just don’t have enough energy to get through that on-land period,” said Derocher. As climate change warms the Arctic faster than anywhere else on Earth, that ice-free period is lengthening, though some regions are hit harder than others.
“There's a huge amount of variation between these areas in how fast the sea ice is disappearing,” Derocher explained.
Since the 1980s, the Norwegian Arctic, for instance, has been losing more than 30 days of ice cover per decade. Off the coast of Alaska, the Southern Beaufort Sea is losing about 12 to 18 days of sea ice cover. In Churchill, Manitoba — the “polar bear capital of the world” — is only losing about 6 to 12 days per decade, said Derocher
The impact of that sea ice loss on polar bears in any given area depends on a range of factors. Consider Alaska’s two polar bear populations. One lives near the Beaufort Sea, where seals inhabit a narrow strip of shallow water that quickly drops off into deep, inhospitable sea. “If you take ice away from that area, you’re taking food away from the bears,” said Derocher. Consequently, that population — currently less than 1,000 bears — declined by about 50% over the past three decades.
Alaska’s other population lives along the Chukchi Sea between Alaska and Russia’s northern coasts. There, seals are abundant throughout the shallower sea. While sea ice is declining, the Chukchi Sea polar bears are fairly stable because the relative abundance of food in that environment gives them more of a buffer.
In the Kane Basin, which sits between the northernmost reaches of Canada and Greenland, warmer weather is proving beneficial, albeit temporarily, to some populations.
Historically, frigid conditions keep the Kane Basin's ice 15 feet thick, preventing seals from being able to come up for air. But as the region warms, “we’re seeing this — probably transient — phenomenon where the ice went from too thick to just right,” said Eric Regehr, a biologist at the University of Washington. “It’s not as harsh a polar desert as it once was, though the same forces that brought ice from too much to just enough will eventually drive it to too little.”
Individual polar bear populations will vary in their response to climate change, but when scientists zoom out, the picture is still dire — especially if climate–warming emissions don’t come down.
OVER THE NEXT 30 years, Regehr and his colleagues estimate that the global polar bear population could decline by around 30% even if we started drastically reducing emissions.
“There’s a lot of momentum in the system,” said Regehr. “If you look at how the ice is projected to change, there’s not much difference between business as usual versus mitigation in the next 30 years.”
Further out, the possible fates of polar bears start to “diverge hugely,” he said. “We can’t say that in the next 100 years, X.Y% of bears will remain in a given region, we don’t have that level of specificity, but it’s pretty clear that the choice of which greenhouse gas emissions we follow has a huge impact on how these animals will fare.”
Under high greenhouse gas emissions scenarios, some researchers suspect that all but the most northerly polar bear populations will go extinct by 2100: There simply won’t be enough sea ice to support them. Further south, it will become increasingly hard to find food. Cubs won’t be able to survive, and the populations will slowly dwindle as bears die out.
Part of the problem is that polar bears’ ability to adapt to an ice-less life is limited, Regehr explained. “On land, they could graze on sedges and grasses, but that doesn’t work very well because their digestion is purely keyed in on carnivory,” he said. Polar bears have been observed eating caribou or reindeer, but they’re difficult to catch.
“They’re ambush predators, not pursuit predators,” said Regehr. The occasional rodent or lemming could help, but polar bears can’t subsist solely on such small fare.
As polar bears move north and their numbers shrink, a string of bad years — unusual warmth, an oil spill, or some other kind of environmental disaster — could spell the end. “With smaller populations, you can lose animals much faster, increasing the chances that some catastrophic event will cause them to blink out in a given area.
Polar bears’ outlook improves slightly under more optimistic emissions reduction scenarios, though some southern populations will probably disappear.
Whether, or how quickly, that happens will depend in part on local conservation efforts.
With less sea ice, polar bears are venturing onto land more often, which can raise tensions with local communities. “Human safety is obviously huge, but it’d also be nice to not kill every bear that gets too close to people,” said Regehr, pointing to non-lethal deterrence strategies.
Local Indigenous communities also play a key role in managing polar bear populations. The Alaska Nannut Co-Management Council works with the U.S. Fish and Wildlife Service in developing strategies to ensure sustainable polar bear populations while allowing subsistence hunting, which is a vital part of many Indigenous cultures.
Such efforts are important, but won’t be enough to ultimately save polar bears in the face of climate change, said Regehr. “If the goal is to keep polar bears around for 1,000 years, climate mitigation is necessary.”
Of course, it’ll be more than just polar bears that suffer in a warmer world. “By the time polar bears are in really dire straits, no one’s gonna be thinking about polar bears,” said Regehr.
“They’re important and powerful symbols for the effects of climate change," but he suspects the social, economic and humanitarian crises associated with not addressing climate change will drown out concerns over these iconic masters of a vanishing Arctic.